Conventional bicycle frames are assemblies built from individual tubes which are secured together by welding, brazing or by using other means for joining the tubes. In naming the structural components of bicycle frames, the individual frame tubes were designated by their location in relation to the other major components or assemblies used to make up the functioning bicycle. Thus, it was that the short frame tube which supported the handlebar assembly and the front wheel fork was referred to as the "head" tube, the tube which supported the seat and connected to the pedal axle support (the bottom bracket) was referred to as the "seat" tube, the tube which joined the top of the seat tube and the head tube was referred to as the "top" tube, the tube which descended from the head tube to the bottom bracket was referred to as the "down" tube, the pair of tubes which descended from the seat tube to the ends of the rear wheel axle, with one tube on either side of the rear wheel, were referred to as the "seat stays", and the pair of tubes which connected the bottom bracket to the ends of the seat stays at the rear wheel axle, with one tube on either side of the rear wheel, were referred to as the "chain stays".
The multiplicity of connections required to secure these individual structural parts together, combined with the different forces encountered by the bicycle as it is ridden, cause a variety of problems. It is not unusual, for example, for one or more of the joints or connections on a conventional bicycle frame to fail, making the entire frame unsuitable for use until the connection is repaired. For many frames, the cost of straightening the frame and repairing the connection is prohibitive.
Further, the individual tubes and associated joints are relatively heavy since the tubes are generally made by the extrusion of or by the rolling and seaming of a metal alloy, and the joints are generally made by welding or brazing these tubes together. The manufacture and assembly of these multiple structural parts is also time consuming and costly. Certain problems with conventional bicycle frames and their construction methods have been previously addressed. For example, U.S. Pat. No. 3,833,242 to Thompson, Jr. discloses a frame having a hard exterior skin molded as a unitary piece over a structural foam interior. The frame was constructed by techniques disclosed in U.S. Pat. Nos. 3,268,636 and 3,456,446 to Angell, Jr.
In addition, U.S. Pat. No. 4,513,986 to Trimble discloses a monocoque type frame having a stressed, unitary outer skin over internal stiffening ribs and other structural elements. Other molded frames and construction methods appear in U.S. Pat. Nos. 3,233,916; 3,375,024; 3,884,521; and 4,015,854, and in U.K. Patent No. 1,361,394.
These frames may provide advantages over conventional bicycle frames, due in some instances to increased strength and a reduced number of major structural joints. However, these frames generally require the interconnection of large number of interior structural support elements such as shear webs, reinforcing angles, reinforcing blocks and strips, and joining blocks, and/or the presence of structural foam in the interior to support the frame, thus sharing certain deficiencies with conventional frames. In addition, the construction methods employed therein are labor intensive and do not appear readily adaptable to efficient mass production.
Thus, it was perceived that some of the above problems could be remedied by a bicycle frame which is constructed from inexpensive, lightweight and strong composite materials.
Ideally, the frame would be easy to construct and adaptable to mass production techniques. It therefore was considered desirable to provide an improved method for producing a generally hollow bicycle frame made from resin composite materials.